Toners are required to have a good heat-resistant storage property and a good low-temperature fusing property which are contradictory to each other. In order to satisfy both the contradictory properties, there have been proposed toners having a core-shell structure including a core portion and a shell portion covering the core portion.
For example, Patent Document 1 discloses a resin binder for toners in the form of core-shell particles each including a core portion containing an amorphous resin obtained by polycondensing a carboxylic acid component containing at least one of an alkyl succinic acid and an alkenyl succinic acid with an alcohol component, and a crystalline polyester, and a shell portion containing an amorphous resin obtained by polycondensing an alcohol component containing an aliphatic dialcohol with a carboxylic acid component. In Patent Document 1, it is described that the reason why the alkyl succinic acid or the like is used as the carboxylic acid component of the amorphous resin constituting the core portion is that the crystalline polyester contained in the core portion can be finely dispersed in the amorphous resin constituting the core portion and enclosed in the core-shell structure so that the resulting toner can be enhanced in high anti-staining property for carriers and charging rate.
Also, in Patent Document 2, it is described that when using an alkyl succinic acid or an alkenyl succinic acid as a carboxylic acid component of an amorphous resin of a core portion, it is possible to enhance a compatibility between the amorphous resin and a crystalline polyester contained in the core portion.
Patent Document 3 discloses a process for producing a toner which includes a first aggregation step of aggregating resin fine particles containing an amorphous polyester resin to produce a dispersion of a first precursor of toner particles, a mixing step of mixing the dispersion of the first precursor of toner particles with a dispersion of carboxyl group-containing polyester resin fine particles to produce a dispersion of a second precursor of toner particles, and a second aggregation step of aggregating the second precursor of toner particles to form toner particles for the purpose of enhancing a low-temperature fusing property, a heat-resistant storage property, an anti-breaking property and an anti-filming property of the resulting toner and suppressing occurrence of dusts and scattering of the toner.
Patent Document 1: JP 2011-197193A
Patent Document 2: JP 2011-197192A
Patent Document 3: JP 2010-145611A